Transmit Efficiency

I tested several small rigs for power consumption in CW mode with a straight key. Power was provided by a linear lab bench supply that displays voltage and current and RF out measured by a Barb-a-watt meter using its dummy load. The testing was done on 20 meters at around 5 watts except for the monoband QCX that was at 40 meters. Most rigs were run at 12 V except for the xBitx that runs at 9 V.

In each case the current draw on receive and transmit were recorded, power computed and for transmit an efficiency assigned by dividing RF out watts by input DC watts.

In the last column I note whether the rig can carry a built in battery.

Summary:

I think about these rigs in three groups:

First group

Small package, SDR, class E amp, small monochrome display

Designed for maximum portability and efficiency.

These are all related to the small, highly efficient QRP Labs QCX monoband transceivers.

I tested the QMX+ which has a larger case, but the standard QMX is the same size as the QCX mini. The QMX+ has development space inside the case and a group has designed a battery pack and tuner to fit in.

The (tr)uSDX has a tiny monochrome spectrum display function

Second group

Larger package, analog design, class AB amp, small monochrome display

A bit larger with more traditional analog design. The TR-45 is the largest package of the rigs tested.

Third group

Larger package, SDR, larger display, some with color

The zBitx and FX-4CR have color displays with a spectrum.

Note that I retested the KX3 at about 10 watts and the efficiency went up a bit.

The transmit efficiency of the zBitx is particularly low and the back plate heat sink gets noticeably hot quickly.